In electronic circuits, bypass capacitors provide impedance paths for alternating currents so that the high frequency alternating currents are not transmitted to selected portions of the electronic circuit. On printed circuit boards, various types of discrete electrical components having various configurations and electrical connection arrangements have been employed as bypass capacitors.
For example, a discrete capacitor well known in the art is the axial lead capacitor which is cylindrical in shape and has an electrical lead extending from each of the flat ends of the cylinder. Axial lead capacitors are typically installed on the printed circuit board by bending the leads away from the capacitor so that when the capacitor is placed on the circuit board along its longitudinal side, the leads make contact, either by feed through or surface mount, with corresponding circuit traces etched on the printed circuit board.
A second type of capacitor well known in the art is the tombstone capacitor which is configured in the shape of a box having electrical leads extending from only one of the faces of the box. Like the axial capacitor, the leads of the tombstone capacitor must also be bent in order to make contact with circuit traces on the circuit board.
The third type of capacitor known in the art is a leadless capacitor used for surface mounting to a printed circuit board. The leadless capacitor is configured in the shape of a box having electrical contacts disposed on one face of the box. The leadless capacitor is electrically connected to the printed circuit board by soldering each electrical contact of the capacitor to a respective circuit trace on the printed circuit board.
Since high performance electronics operate at increasing frequencies, it becomes necessary to include the capacitance of both the circuit traces on the printed circuit board and electrical leads of the capacitors when designing an electronic circuit. In order to avoid or minimize the capacitance effects of the capacitor leads, the circuit designer will seek to place the bypass capacitors employed in the circuit as close as possible to the corresponding integrated circuit package. However, as the frequency of operation of the electronic circuits increases, the circuit designer also attempts to place the integrated circuit packages as close together as possible on the printed circuit board. Thus, in the design and manufacturing of the electrical circuit, both the bypass capacitors and the integrated circuit packages compete with each other for placement close to other integrated circuit packages on the printed circuit board.
Consequently, in order to accommodate the need to both reduce undesired circuit capacitance due to capacitor leads and use space more efficiently, circuit designers have elected to incorporate bypass capacitors into the printed circuit board itself. The design of such a bypass capacitor avoids need for electrical leads and, therefore, eliminates the undesired contribution of capacitance inherent with such leads. In effect, the leads are part of the capacitor. Additionally, the design of such a bypass capacitor, built as an integral member of the printed circuit board, facilitates the efficient use of space in designing an electrical circuit.
However, the advent of high performance computers has also created a greater need for high density conductors within the printed circuit board without an increase in the complexity and cost of manufacturing. Thus, in a manner similar to the competition for space for components mounted on the surface of the printed wiring board (i.e., integrated circuits and capacitors), bypass capacitors fabricated as integral printed circuit board components also compete for space with the high density conductors within the printed circuit board itself.
Accordingly, the need exists for a capacitor that is both small in size to permit its use in high performance computers and is configured having electrical connectors that do not contribute significantly to the capacitance of the capacitor. Unfortunately, the basic construction of a capacitor, comprising conductive members electrically separated by a nonconductive layer, inherently limits the ability to reduce the size of capacitor. This is due to electrical short circuits that may occur between conductive members due to the particular thickness of the nonconductive layer and/or particular configuration of the conductive members. For example, electrical shorts in capacitors made from thin films of conductive materials electrically separated by a dielectric layer are known to be caused at interfaces between the conductive members and the dielectric layer where there exists sharply deflecting topography.
It is, therefore, desirable that a bypass capacitor be fabricated in such a manner that will facilitate its spatially efficient use with a printed circuit board comprising numerous integrated circuits. It is desirable that the bypass capacitor be fabricated in such a manner that will minimize the undesired capacitance contribution associated with the means used to electrically connect the capacitor to a printed circuit. It is desirable that the capacitor be fabricated in a manner that minimizes the potential for electrical shorts between conductive members forming the capacitor. It is also desirable that the method of manufacturing the bypass capacitor, as well as the materials used, be both practical and economically feasible.